Add a "list<regex>" config option and move regex config to it

Summary:
Fixes T3807. Several issues:

• Currently, we split config of type list<string> on commas, which makes it impossible to enter a regex with a comma in it.
  • Split on newlines only.
• Some of the examples are confusing (provided in JSON instead of the format you actually have to enter them).
  • Show examples in the same format you should enter text.
• We didn't validate regexps.
  • Introduce list<regex> to validate regexes.

@hlau: Note that the old config format for the bugtraq stuff implied the delimiters on the regular expression. They are no longer implied. The examples show the correct format.

Test Plan: Viewed and edited affected config, hitting error and success cases.

Reviewers: btrahan

Reviewed By: btrahan

CC: hlau, aran

Maniphest Tasks: T3807

Differential Revision: https://secure.phabricator.com/D6969